I. Field of the Invention
The present invention relates generally to the field of mapping and ablation using steerable vascular catheters. The invention is particularly directed to an atrial mapping and ablation catheter system for the creation of linear continuous lesions.
II. Discussion of the Related Art
Steerable catheter systems of several types have been devised. Such devices can be inserted into blood vessels or similar bodily areas and their distal ends navigated through the tortuous vascular path to reach areas of the body normally inaccessible without surgery. Catheters of the steerable or self-navigating type, having distal electroded sections for monitoring parts of the body, such as for electrically mapping the heart by receiving and transmitting electrical signals related to the operation of that organ to recording signal processing and display devices are also known. The ability to successfully record impulses or signals and from them electrically map the cardiac chambers and valves using flexible catheters having steerable electroded tips has further led to the use of the technique of transcatheter ablation of cardiac tissues that have been identified as the pathways that cause cardiac arrhythmias. This technique has emerged as one of the most important advances in cardiac electrophysiology. Its goal is to destroy the arrhythmogenic tissue without compromising the mechanical or muscular integrity of the cardiac tissues and vessels.
Not long ago, for example, many patients with Wolff-Parkinson-White syndrome or ventricular tachycardia underwent surgical dissection of the arrhythmogenic tissue followed by a painful and prolonged recovery. Introduction of the transcatheter approach has dramatically reduced the suffering and cost of this definitive treatment for many causes of cardiac arrhythmias.
The general approach to this procedure initially preferably utilized high energy direct current delivered to the catheter poles, for example, to disrupt the A-V node condition and even to create a complete heart block by ablating the His bundle. More recently, however, radio frequency has replaced high energy direct current as the preferred primary source of energy and the transcatheter approach for cardiac ablation has become an accepted and common procedure and has been used increasingly as the primary mode of treating cardiac arrhythmias. Transcatheter cardiac tissue ablation is more fully discussed in Avitall et al, "Physics and Engineering of Transcatheter Tissue Ablation", JACC, Volume 22, No. 3:921-32. The rapid clinical acceptance of this procedure and the proliferation of physicians engaged in transcatheter tissue ablation has mandated the development of improved steerable catheter devices.
Other common cardiac arrhythmias untreatable except with medication, and more recently, surgery, involve atrial fibrillation and flutter. These conditions, in fact, are the most common rhythm disturbances in human beings. For example, approximately 1% of the population of the Unites States, i.e., more than 2.5 million people, depends on medication to control this condition. These irregular heart rhythms can reach rates of 180 beats/minute or more. The resulting loss of blood flow due to incomplete atrial contractions along with a rapid heart rate can lead to shortness of breath, dizziness, limited physical endurance, chest pains, in patients with coronary heart disease, and other related problems.
Recently, Dr. Cox et al of Washington University School of Medicine in St. Louis, Miss., have devised a surgical procedure called the Maze and Corridor operation. This procedure is an attempt to restore the normal heart rhythm by segmenting the atrial tissues in a manner that allows the normal heart pacemaker to conduct to the AV node as well as preventing the atrial tissues from sustaining the atrial fibrillation. By cutting the atrial tissue, no electrical activity can be transmitted from one segment to another, thus making the segments too small to be able to sustain the fibrillatory process. The approach, while successful, has the same drawbacks as other previous surgical approaches with respect to the recovery of the patient. This represents another area of cardiac arrhythmic treatment where a more benign approach, i.e., without invasive surgery, would represent a definite advance.
In this regard, as with certain other arrhythmia conditions, electrical decoupling of tissues by heating the tissues with radio frequency (RF) energy, microwave energy, laser energy, freezing and sonication, represent possible alternative approaches. Heating tissues above 55.degree. C. is known to cause permanent cellular injury, making the cells electrically silent. It has been found that segmenting tissues by creating continuous linear lesions via ablation in the atria mimics some aspects of the maze and corridor procedure. The most important aspect of these lesions is their transmural and continuous character; otherwise, segmenting the heart and preventing atrial fibrillation would not be possible. However, it is possible that limited division of tissues within the right atrium may prevent atrial fibrillation in some patients. Furthermore, segmenting a corridor between the sinus node and the AV node will maintain physiological control of heart rate despite the fibrillation of the atrial tissues.
Present steerable catheter systems, while successful in addressing many internal cardiac areas, have not been so successful in treating atrial fibrillation because they have not been able to contact certain surface areas of the right atrial chamber without great difficulty. In this regard, prior devices have failed to successfully create the necessary linear lesions via ablation to achieve the desired segmentation. The provision of a mapping and ablation catheter system that can successfully treat atrial fibrillation and flutter as by readily creating linear continuous lesions in the atria would represent a definite advance in the treatment of this condition.
Accordingly, it is a primary object of the invention to provide an improved catheter, easily deployed and maneuvered to contact desired inner wall surfaces of the right atrial cardiac chamber and sustain contact so that linear lesions can be produced as required.
Another object is to provide multi-electrode working catheter shapes that are easily deployed from sheaths or main catheters once the desired atrial chamber is reached.
An additional object of the invention is to provide such catheter shapes capable of being readily modified to address internal surfaces of varying contour in a linear manner.
Yet another object of the invention is to provide a method of readily mapping and ablating in the right atrial chamber.
Other objects and advantages of the invention will become apparent to those skilled in the art in accordance with the descriptions and Figures of this specification.